In today's perpendicular magnetic recording (PMR) technology, an all wrapped around (AWA) shield writer is widely used by the major hard disk drive (HDD) manufacturers. The function of a trailing shield in an AWA structure is to improve the magnetic field gradient along a down track direction which is a key requirement for high bits per inch (BPI). Meanwhile, side shields and a leading shield serve to define a narrower writer bubble which is important for realizing higher tracks per inch (TPI). In order to achieve higher area density (i.e. higher BPI and TPI) in advanced writer designs, the gap between the main pole and all shields, including the write gap adjoining the trailing shield, side gaps adjacent to the side shields, and lead gap next to the leading shield must be as narrow as possible. However, the material used for conventional AWA shields is a soft magnetic material without preferred anisotropy. Therefore, narrowing the gap between a shield and main pole will only lead to an unwanted flux path from the main pole to the shield which in turn reduces the writability (magnetic field) of the writer on magnetic recording media. This dilemma is considered one of the most significant challenges to improving current writer designs and performance.
Referring to FIG. 1, internal flux loss is depicted in a conventional PMR writer 1 comprising a main pole 11 and shield 12 that can represent a trailing shield, side shield, or leading shield depending on the direction of movement of the writer over magnetic medium 10 during a write process. Magnetic charges 7a, 8a of opposite sign are shown on an air bearing surface (ABS) side of the shield 12, and main pole 11, respectively, and are responsible during a write process for the preferred direction 5 of flux Bs1 from the main pole to the magnetic medium, and returning from the magnetic medium to the shield. Magnetic flux Bs0 is provided to the main pole from coils (not shown). As the gap (distance) between main pole and shield becomes smaller, flux loss Bs2 in a direction 6 from main pole to shield becomes more severe due to magnetic charges 7b, 8b on opposing sides of the shield, and main pole, respectively. Consequently, the write field Bs1 on the magnetic recording medium will be degraded. With the constraint of write field amplitude on the magnetic medium 10, further reduction of the gap between main pole and shields is not allowed which limits achieving a higher recording area density. Thus, an improved shield design is needed to minimize flux loss Bs2 and maximize write field Bs1.
A search of the prior art revealed the following references. U.S. Pat. No. 7,791,844 discloses magnetic shields having magnetic anisotropy with easy axes of magnetization that are oriented substantially perpendicular to the track direction. The magnetic anisotropy is created by one or more surface texture treatments such as ion milling and prevents the NiFe shields from becoming saturated in a direction perpendicular to the magnetic recording medium.
U.S. Pat. No. 7,697,244 teaches that a CoFe shield may be stabilized to have a single domain status when no fields are applied. The uniaxial anisotropy field HK is about 7.5 Oe which corresponds to a permeability of about 1400 and means a large amount of magnetic flux from the magnetic medium can penetrate into the shield.
U.S. Patent Application 2010/0221581 describes a method of fabricating a recording medium wherein the c-axis is aligned along the easy axis.
A. Hashimoto et al. describe the use of a negative Ku magnetic material in “A soft magnetic underlayer with negative uniaxial magnetocrystalline anisotropy for suppression of spike noise and wide adjacent track erasure in perpendicular magnetic recording media”, Journal of Applied Physics, 99, 08Q907 (2006).
A composite grain of easy plane material (CoIr with negative Ku) and perpendicular anisotropy material (CoPt with positive Ku) are used in a magnetic medium to improve the head field gradient and amplitude as described by Park et al in “A novel crystalline soft magnetic intermediate layer for perpendicular recording media”, Journal of Applied Physics, 105, 07B723 (2009), and in “Co-7% Ir Soft Magnetic Intermediate Layer for Perpendicular Media”, IEEE Transactions on Magnetics, Vol. 46, No. 6, June 2010.
Takahashi et al. discuss structural and magnetic analyses of a′-Fe—C films in “Magnetocrystalline Anisotropy for a′-Fe—C and a′-Fe—N Films”, IEEE Transactions on Magnetics, Vol. 37, No. 4, July 2001.